ASHRAE Journal - August 2022 - 18
TECHNICAL FEATURE
Saving Money with
Real-Time VAV Control
Optimization
BY ANDREW MARTIN, ASSOCIATE MEMBER ASHRAE
Outdoor airflow into a building is necessary for occupant health and comfort, but
conditioning it requires large amounts of energy and makes overventilation an
expensive problem. However, in variable air volume (VAV) systems a way exists to
reduce this cost by increasing the efficiency of how the ventilation air is distributed.
The secret is to oversupply discharge air to certain zones, despite the reheat penalty
incurred by doing so. This counterintuitive notion reveals a trade-off in how energy
can be consumed in different parts of the system. Advanced control systems can take
advantage of this dynamic to optimize system setpoints in real time, yielding significant
energy cost savings.
The optimal control scheme in this article was
designed for single-duct VAV systems with terminal
reheat, and it is applicable to systems both with and
without demand-controlled ventilation. It may be suitable
for other types of VAV systems, though these have
not yet been investigated.
The Core Trade-Off of HVAC
According to the acronym itself, HVAC systems support
heating, ventilation and air conditioning. In terms
of energy efficiency, though, it is the " and " part that is
one of their biggest drawbacks. Trying to satisfy all three
of these goals at the same time with a single airstream
Andrew Martin is the founder of Grissom Controls, LLC.
18
ASHRAE JOURNAL ashrae.o rg
A U G UST 2022
necessarily creates inefficiencies, such as overventilation
and simultaneous heating and cooling. Eliminating
these inefficiencies turns out to be a trade-off of energy
costs versus capital and maintenance costs. Moreefficient
designs are typically more complex and thus
more expensive to purchase and maintain. For instance,
dedicated outdoor air systems attempt to decouple
ventilation and heating/cooling requirements, but they
do so by duplicating components for each purpose. On
the other hand, simple designs like constant air volume
systems are cheaper and easier to install and maintain,
but they can be energy hogs and therefore are generally
not allowed by energy efficiency codes. On both of these
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ASHRAE Journal - August 2022
Table of Contents for the Digital Edition of ASHRAE Journal - August 2022
Contents
ASHRAE Journal - August 2022 - Intro
ASHRAE Journal - August 2022 - Cover1
ASHRAE Journal - August 2022 - Cover2
ASHRAE Journal - August 2022 - 1
ASHRAE Journal - August 2022 - Contents
ASHRAE Journal - August 2022 - 3
ASHRAE Journal - August 2022 - 4
ASHRAE Journal - August 2022 - 5
ASHRAE Journal - August 2022 - 6
ASHRAE Journal - August 2022 - 7
ASHRAE Journal - August 2022 - 8
ASHRAE Journal - August 2022 - 9
ASHRAE Journal - August 2022 - 10
ASHRAE Journal - August 2022 - 11
ASHRAE Journal - August 2022 - 12
ASHRAE Journal - August 2022 - 13
ASHRAE Journal - August 2022 - 14
ASHRAE Journal - August 2022 - 15
ASHRAE Journal - August 2022 - 16
ASHRAE Journal - August 2022 - 17
ASHRAE Journal - August 2022 - 18
ASHRAE Journal - August 2022 - 19
ASHRAE Journal - August 2022 - 20
ASHRAE Journal - August 2022 - 21
ASHRAE Journal - August 2022 - 22
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ASHRAE Journal - August 2022 - 24
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ASHRAE Journal - August 2022 - 27
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ASHRAE Journal - August 2022 - Cover3
ASHRAE Journal - August 2022 - Cover4
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